title: In pursuit of individualised margins for prostate cancer patients undergoing image-guided radiotherapy: the effect of body mass index on intrafraction prostate motion.
abstract: OBJECTIVE
  To analyse the relationship between body mass index (BMI) and intrafraction displacement in patients undergoing prostate cancer image-guided radiotherapy.
  
  
  METHODS
  An analysis was carried out on 151 prostate cancer patients treated with radical dose radiotherapy between January 2007 and March 2009. Patients had their height, weight and daily intrafraction prostate displacement data collected prospectively during fiducial marker image-guided radiotherapy with orthogonal imaging. For each of anterior-posterior, left-right and superior-inferior axes, a univariable linear regression analysis was carried out with the individual patient standard deviation of shift as the response variable and BMI as a continuous explanatory variable.
  
  
  RESULTS
  Displacement measurements were recorded from 4764 pre- and post-treatment image sets. Patients were grouped according to BMI as normal weight (24%), overweight (52%), obese (18%), severely obese (3%) or morbidly obese (3%). For intrafraction displacement, a one unit increase in BMI affected the standard deviation of shift by: anterior-posterior -0.02 (95% confidence interval -0.040 to 0.000), left-right -0.006 (95% confidence interval -0.020 to 0.008) and superior-inferior -0.020 (95% confidence interval -0.037 to -0.003).
  
  
  CONCLUSIONS
  Our data indicate that patients with a higher BMI have less intrafraction displacement of the prostate in the superior-inferior dimension compared with patients with a lower BMI. This has implications for individualised treatment margins for future prostate cancer patients undergoing image-guided radiotherapy. Further study is recommended.
authors.affiliation: Department of Radiation Therapy Services, Peter MacCallum Cancer Centre, Melbourne, Victoria, Australia. Ann.Thompson@petermac.org
authors.forename: A L
authors.initials: AL
authors.lastname: Thompson
authors.forename: S
authors.initials: S
authors.lastname: Gill
authors.forename: J
authors.initials: J
authors.lastname: Thomas
authors.forename: T
authors.initials: T
authors.lastname: Kron
authors.forename: C
authors.initials: C
authors.lastname: Fox
authors.forename: A
authors.initials: A
authors.lastname: Herschtal
authors.forename: K H
authors.initials: KH
authors.lastname: Tai
authors.forename: F
authors.initials: F
authors.lastname: Foroudi
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D009765:Obesity / Q000150:complications; D050177:Overweight / Q000150:complications; D057285:Precision Medicine / Q000379:methods; D011471:Prostatic Neoplasms / Q000150:complications / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided; D050397:Radiotherapy, Intensity-Modulated; D055815:Young Adult